OVERVIEW
Modern automotive systems require low standby power combined with reliable wake-up functions. In applications such as displays, cameras, infotainment systems, and distributed ECUs, subsystems can be activated only when communication activity is detected on a differential data line.
The Vishay VOMA618A optocouplers are well suited for this function, providing galvanic isolation while generating a reliable wake-up or power-enable signal from communication activity.
PRINCIPLE OF OPERATION
An optocoupler can monitor activity on a differential communication interface while providing electrical isolation between the communication domain and the local power-control circuitry.
When communication activity is detected:
• The optocoupler LED is activated
• The output transistor switches
• A wake-up or enable signal is generated
• The subsystem power supply is activated
This approach can be applied to interfaces such as CAN/CAN-FD, LVDS-based links, APIX3, and other differential communication systems, as shown in the figure below, which illustrates a typical wake-up detection circuit using Vishay VOMA618A optocouplers.
ADVANTAGES
• Galvanic Isolation: improves EMC behavior and protects sensitive electronics from disturbances
• Low Standby Power: allows the main subsystem to remain powered down until required
• Simple Integration: the wake-up signal can directly control PMIC enable pins, load switches, MOSFET stages, or ECU wake-up inputs
• Improved System Robustness: reduces fault propagation between communication and power domains
DESIGN CONSIDERATIONS
Important parameters include communication signal amplitude, optocoupler CTR tolerance, switching thresholds, filtering, and wake-up response time. RC filtering may be added to avoid false triggering caused by noise or transient signals.
CONCLUSION
Optocoupler-based wake-up detection provides a simple, isolated, and robust solution for automotive low power architectures. It enables reliable subsystem activation while improving EMC performance and system protection.